circadian
adjective
cir·ca·di·an
sər-ˈkā-dē-ən 
: being, having, characterized by, or occurring in approximately 24-hour periods or cycles (as of biological activity or function)
circadian rhythms in activity
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In 1959, a scientist formed the word circadian from the Latin words circa ("about") and dies ("day"), and it caught on quickly. Most often, it's seen and heard in the term circadian rhythm, which refers to the inherent cycle of about 24 hours that appears to control various biological processes, such as sleep, wakefulness, and digestive activity. If you want to impress your friends, you can also use the term circadian dysrhythmia, a fancy synonym of jet lag.
Examples of circadian in a Sentence
Recent Examples on the Web
Women’s Health Network notes that hormonal fluctuations trigger cortisol release that actively derails the circadian sleep cycle, and women in this transition are more vulnerable to adrenal stress responses than at any other life stage.
—
Allison Palmer, Kansas City Star, 1 Apr. 2026
Hormonal fluctuations trigger cortisol release that derails the normal circadian sleep cycle, and women in this transition are more vulnerable to adrenal stress responses.
—Allison Palmer, Sacbee.com, 1 Apr. 2026
Along with glowing skin and greater scalp health, the brand claims that the showerhead can boost circulation and mood while supporting the circadian rhythm for sounder sleep.
—Jenny Berg, Vogue, 31 Mar. 2026
Melatonin is a hormone your body naturally produces that regulates your circadian rhythm (sleep–wake cycle).
—Lindsay Curtis, Verywell Health, 31 Mar. 2026
See All Example Sentences for circadian
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Allison Palmer, Kansas City Star, 1 Apr. 2026
Hormonal fluctuations trigger cortisol release that derails the normal circadian sleep cycle, and women in this transition are more vulnerable to adrenal stress responses.
—Allison Palmer, Sacbee.com, 1 Apr. 2026
Along with glowing skin and greater scalp health, the brand claims that the showerhead can boost circulation and mood while supporting the circadian rhythm for sounder sleep.
—Jenny Berg, Vogue, 31 Mar. 2026
Melatonin is a hormone your body naturally produces that regulates your circadian rhythm (sleep–wake cycle).
—Lindsay Curtis, Verywell Health, 31 Mar. 2026
See All Example Sentences for circadian
Cite this Entry
“Circadian.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/circadian. Accessed 5 Apr. 2026.
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circadian
adjective
cir·ca·di·an
(ˌ)sər-ˈkad-ē-ən, -ˈkād-; ˌsər-kə-ˈdī-ən, -ˈdē-
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